Seminar Series Events/Videos

Massive neutral fermions can be realized in Nature as Majorana particles. Are neutrinos Majorana particles? Our most accepted theoretical prejudice can be verified by searching for neutrinoless double-beta decay. I will overview the current knowledge of the neutrino mass spectrum and discuss theoretical scenarios where cosmological data can contribute to resolve this challenging question. Some cosmological observables sensitive to neutrino masses are outlined.

There have been recent claims that the weak gravity conjecture (WGC) rules out multi-field natural inflation. I review these claims and then show how 2-field natural inflation can be consistent with even the most stringent form of WGC. I also discuss my recent attempt at numerically proving the WGC via the conformal bootstrap.

Super-massive black holes that grow at the center of dark matter halos distort the dark matter within their zone of influence into a steep density spike. This spike can give rise to strong enhancements of standard indirect detection signals, and can lead to qualitatively new windows onto the physics of the early universe. I will talk about potential dark matter signals from the Milky Way's central black hole, some astrophysical caveats, and the possible use of black holes as dark matter accelerators.

Recent landmark measurement of the muonic hydrogen Lamb shift generated more questions than answers, as it stands in a sharp disagreement with what was predicted based on known properties of muons and protons. It adds on top of the existing anomalies in the muon sector (discrepancy in g-2 and in radiative muon capture). I will critically review some suggestions for the new physics explanations of these anomalies, and describe their implications.

Astrophysical observations suggest that the majority of matter in the Universe is made up of novel Weakly Interacting Massive Particles (WIMPs). Such WIMPs are often predicted by extensions to the Standard Model. Efforts have been underway for more than two decades to detect WIMPs directly in detectors on earth. The challenge is great because of the small energies involved and the low interaction rates. The field has been driven by progress in detectors able to identify radioactive backgrounds.

Can we learn about New Physics with astronomical and astro-particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental, particle nature of the dark matter.

Astrophysical observations of the structure of galaxies and clusters are no longer simply proving the existence of DM, but have sharpened into a discovery tool probing the particle physics of dark matter. I discuss small scale structure anomalies for cold dark matter and their possible implications for dark matter physics, such as the existence of forces in the dark sector. New results on cluster scales provide a new important handle for constraining dark matter's particle interactions.

As an experimentalist involved in the search for physics beyond the Standard Model at the LHC, one must choose carefully which signatures to pursue. While theoretical guidance in identifying well motivated gaps in the coverage of “natural” BSM extensions is an important ingredient in this choice, unexplored territory is often unexplored for a reason, namely that there are likely non-trivial (“tricky”) experimental difficulties. One must thus consider the risk (time) vs. reward (discovery) in deciding what to pursue.

The presence of an instability in the Standard Model Higgs potential may have important implications for inflation and the viability of our Universe. In particular, if the Hubble scale during inflation is comparable to (or larger than) the instability scale of the potential, quantum fluctuations in the Higgs field will lead to the Higgs sampling the unstable part of the potential during inflation. However, to correctly study transitions to the unstable regime and determine the significance for the resulting universe requires addressing a number of subtleties.